The present disclosure relates to a memory element having a high-resistance layer and an ion source layer between two electrodes, in which mainly a resistance value of the high-resistance layer is changed by voltage application and to a memory device having the In information devices such as a computer, a DRAM (Dynamic Random Access Memory) of high density and capable of operating at high speed is widely used. However, the DRAM has a problem of high manufacturing cost since the manufacturing process is complicated as compared with general circuits such as a logic circuit and a signal processing circuit used for an electronic device. Further, the DRAM is a volatile memory in which information disappears when the power source is turned off and refresh operation has to be performed frequently.
Then, as nonvolatile memories in which information does not disappear even when the power source is turned off, for example, an FeRAM (Ferroelectric Random Access Memory), an MRA (Magnetoresistive Random Access Memory), and the like are proposed. In those memories, written information is held for long time without supplying power and, since it is unnecessary to perform the refresh operation, the power consumption can be decreased only by the amount. However, in the above-mentioned nonvolatile memories, as the size of memory cells decreases, it is becoming difficult to assure the characteristics of the memories. Then, as memories adapted to miniaturization of memory cells, for example, memory elements of novel types described in patent document 1 and non-patent documents 1 and 2 are proposed.
For example, in memory elements described in the patent document 1 and the non-patent document 1 (detailed below), an ion source layer containing one kind of metal elements of Cu (copper), Ag (silver), and Zn (zinc) and one kind of chalcogen elements of S (sulfur) and Se (selenium) is provided between two electrodes. One of the electrodes contains the metal element contained in the ion source layer. In the memory element having such a configuration, when voltage is applied across the two electrodes, the above-mentioned metal element contained in the one of the electrodes is diffused as ions into the ion source layer, and the electric characteristic such as a resistance value, a capacitance value, or the like in the ion source layer changes. Consequently, by using the change in the electric characteristic, the memory function can be displayed.
Moreover, in a memory element described in the non-patent document 2, for example, a crystal oxide material layer made of SrZrO3 in which Cr (chromium) is doped is provided between two electrodes. One of the electrodes is made of SrRuO3 or Pt (platinum) and the other electrode is made of Au (gold) or Pt. However, the details of the operation principle of the memory element are unknown.
In the memory elements described in patent document 1 and the non-patent document 1, the characteristics of the ion source layer itself determine the quality of the memory characteristics. The memory characteristics include, for example, operation speeds (write speed and erase speed), erasure characteristics (the ratio between resistance before write/erase operation in the repeating operation is performed and resistance after the write/erase operation is performed, also called erasure resistance recovery characteristic), recording characteristics, data retention characteristics (changes in recording resistance and erasure resistance before and after a heating acceleration test), the number of repeating operation times, and power consumption at the time of recording/erasure. However, many of them have a tradeoff relation at the time of adjusting the composition ratio of one element in the ion source layer. Consequently, for example, when the composition ratio of one element in the ion source layer is adjusted for the purpose of improving write speed, there is a case that the erasure characteristic deteriorates. Like this case, there is a problem such that only by adjusting the composition ratio of one element in the ion source layer, it is not easy to improve the characteristics having a tradeoff relation at the same time. To address the problem, for example, in patent document 2, a method of improving the data retention characteristic by also providing a high-resistivity layer (oxide layer) is used.